The present invention relates generallly to agricultural implements, and more specifically, to depth sensing devices for automatic depth control systems which adjust the depth of penetration of ground working tools on an implement.
Automatic depth control systems for tillage and planting implements have become more popular in recent years and are utilized to maintain a constant depth of penetration of the ground engaging tools with varying soil, terrain and load distribution conditions. On seeding and fertilizing implements which utilize a hopper carrying granular material, the weight of the implement changes significantly as the hopper depletes thereby changing the down-pressure on the tools and resulting in depth variations. To overcome problems of depth variation, ground sensing devices are spaced along the width of the implement and are connected through automatic control systems which maintain implement height at a preselected level to provide more uniform depth control.
Various types of height sensing structure have been suggested including noncontacting devices such as optical and acoustic distance sensing devices, but these usually require complex electronic circuitry and can often malfunction in the hostile environment encountered by an agricultural implement. Ground-contacting types of devices such as a rolling wheel arrangement shown in U.S. Pat. No. 4,355,688 or a skid assembly such as shown in U.S. Pat. No. 4,600,060 are relatively bulky in configuration and are expensive to manufacture. Such devices do not lend themselves to be easily moved in the reverse direction and such movement can damage them and render them ineffective. Also, where space is limited on the main frame of an implement, such arrangement of rolling wheels or skids is difficult to mount.